Food Biomolecule Engineering by Unconventional Technological Strategies

Driven by new consumers’ needs, over the last years, food processing shifted from the prior emphasis in process and unit operations to the design of products meeting specific requirements in terms of nutritional, biological and functional properties (tailor made foods). As food structure and functions are closely interlinked, structural changes of food constituents can lead to new product characteristics or improved functionalities. To this regard, different driving forces, such as mechanical or electromagnetic energy, were shown to effectively affect the structure of food proteins or polysaccharides. Taking advantage of specific potentials and opportunities of these unconventional technologies by focusing on the complex process-structure-function relationship, offers the exiting possibility for the development of fresh-like, healthy, tailor made foods. It is evident that this goal can only be reached by clearly understand the effects of the process on biomolecule structure and thus functions. In this context, this PhD thesis aimed to investigate whether and how unconventional technologies, such as light processing and high pressure homogenisation, can be exploited to modify biomolecule structure inducing changes in their own functions as well as in the functions of other bioactives present in the matrix. To this purpose, the thesis was divided in two parts. In the first part, the effect of UV-C and pulsed light on the structure and functions of selected proteins, including polyphenoloxidase (PPO), gluten, and egg white was investigated. In the second part, the effect of high pressure homogenisation on egg white proteins structure and functions as well as on microstructure and carotenoid bioaccessibility (BAc) of tomato pulps was studied. The first part of this PhD research focussed on the effects of light processing on selected proteins which serve important functionalities in foods. In particular, the effect of PL on the structure and enzymatic activity of PPO in model solution, the effect of UV-C light and PL on the structure and technological performances (viscosity, gelling and foaming properties) as well as immunoreactivity of egg white proteins, the effect of PL on wheat gluten structure and immunoreactivity, the effect of PL on wheat starch structure and gelatinization, and the effect of PL on wheat flour microstructure and immunoreactivity was studied. Light processing was found to modify protein structure thus leading to changes in protein functionalities. For instance, pulsed light promoted structural changes of PPO and egg white proteins by means of cleavage and aggregation/unfolding phenomena. The latter led to inactivation of PPO in model systems, better foaming properties but also higher immunoreactivity of egg white proteins. Besides, PL induced structural changes of gluten proteins by means of depolymerisation and unfolding phenomena, leading to the decrease in immunoreactivity of gluten proteins. By contrast, no changes in wheat starch structure and functions could be observed upon exposure to PL. Results relevant to the first part of this PhD thesis show that light processing, based on UV-C light or applied in a pulsed mode, on the one hand can be exploited as a sanitisation treatment without impairing starch performances, and on the other hand it can be regarded as a promising technology to modify protein structure and functions. However, the overall effects of light processing on food biopolymers depend on several factors: i) intrinsic photosensitivity of the target biomolecule (presence of light absorbing sites able to initiate photoreactions), ii) intensity of light radiation, iii) structural arrangement (intra- and inter-molecular interactions occurring , and iv) environmental conditions (crowding effect) experienced by the target biomolecule. These factors should be carefully considered when light processing is intended for modification of protein functionalities. The second part of this PhD research focussed on the effect of HPH processing on food biomolecules. To this aim two different matrices were chosen, namely egg white and tomato puree, as an example of protein- and polysaccharide-containing matrix. Results obtained show that HPH processing can be regarded as a promising technological strategy for improving the functional properties of both proteins and polysaccharides. In the case of egg white, HPH-induced modifications included the destruction of the original protein-protein interactions, protein unfolding, and formation of novel intramolecular interactions between unfolded proteins that resulted in the formation of a weak and unstable network. With regard to fibrous polysaccharides (cell wall polysaccharides in tomato), HPH promoted the interactions between fibres resulting in the formation of a network. The observed protein and polysaccharide structure modifications accounted for different function modifications. With regard to egg white proteins, structure modification did not impair the technological functionalities, but turned out to be sufficient to hide protein epitopes, leading to a slight decrease in egg white immunoreactivity. In the case of tomato pulps, if on the one hand the formation of structure in the food matrix could improve texture, stability and sensory attributes, on the other hand this structure could impair the bioavailability of micronutrients, such as carotenoids. In conclusion, results reported in this PhD thesis show that unconventional technologies, such as light and HPH processing represent promising technological strategies to fulfil the new consumers’ needs towards safe, fresh-like, healthier food products. The choice of the type of processing is driven by the nature of the biomolecule and the expected effect on its structure and functions. Protein and polysaccharide functions can be steered by choosing the proper process with adequate processing conditions. To this regard, the results of this thesis also suggest that the designing of the process should be carefully evaluated on a case by case basis, since undesired effects (i.e. increase in immunoreactivity of proteins or decrease in micronutrients bioaccessibility) may also occur under specific technological conditions. For this reason, understanding the mechanism that control the effect of the process on food structure and functions is crucial for engineering food biomolecule and obtaining foods with the desired characteristics.